The choice of music is questionable - I would strongly recommend something that's "easy listening". No offence, but you absolutely need a mute button. Might be interesting to incorporate some rhythm based-elements to the game for added gameplay depth.
Now I have a hard question about the randomness in the game:
Is it mathematically possible to score purebreds only? I think that would make the gameplay a lot deeper. Not sure, might be more interesting/strategic if you have more than just four slots.purebreds score bonus points